Heat-transfer concentrate, method of manufacturing it and its use as well as a latent-heat accumulator making use of the concentrate

ABSTRACT

A heat-transfer concentrate comprising a storage-stable dispersion of a heat-storage medium and gallium adsorbed onto a solid having either a particle diameter of 1 to 3 um or a pore diameter of 0.2 to 0.6 nm, or both, is provided. The invention also provides a method of manufacture for the concentrate, and a heat-transfer mixture comprising the heat-transfer concentrate and another heat-storage medium. The invention further provides methods of using the heat-transfer mixture to store and convey heat in reactors with heat exchangers, as well as methods of use in heat pumps and as a thermochemical energy-storage medium.

The invention pertains to a heat-transfer concentrate, a process for itspreparation, as well as its use for thermochemical energy storage forproducing chemical heat pumps or for chemical heat transformation, andmoreover, a latent heat-storage device.

In direct utilization of solar energy, for example recovery of heat withsolar collectors, the economic storage of heat (and other energy) inheat-storage devices in which sensible or latent heat can be stored is acentral question, since the heat losses increase with increasing storagetime. Thus, for storage of sensible heat, water constitutes the simpleststorage medium but it is uneconomical for long-term storage devices.Other storage media are latent heat-storage devices that use latent heattaken up and given off during phase transitions such as the heat ofmelting, heat of vaporization, and heat of crystallization.

Latent heat-storage devices are known and contain water, Glauber's salt,natural stone, synthetic stone, or fired alumina such as chamotte as theheat-storage medium. Although water with a specific heat capacity of4.18 kJ/kg·K (kilojoule per kilogram×Kelvin) has the highest specificheat capacity of all elements, a storage temperature of greater than 82°C. is problematical since at this temperature, the minerals dissolved inthe water precipitate and deposit as so-called boiler scale. Due to theboiling point of 100° C. at standard pressure and the resultingincreasing vapor pressure, pressure problems arise with increasingtemperature.

For Glauber's salt, the melting or solidification temperature in theaggregate change of state from solid to liquid or vice versa, fromliquid to solid, must be considered in heat-storage. However, Glauber'ssalt only permits a limited number of aggregate changes of state.Thereafter it remains in the liquid state.

For natural stone materials such as, e.g., basalt, or synthetic stonesor fired alumina such as chamotte, use as a heat-storage device islimited to high temperatures due to the low specific heat capacity.

Heat-transfer fluids (HTF) with addition of metal dusts are known, whichhowever cannot be used in the chemical industry in chemical reactorswith heat exchangers since in case of a tube rupture, there is a highrisk of explosion due to the fine metal particles, especially metalparticles, such as lead or mercury which must not reach the soil due totheir high toxicity.

It was therefore the goal of the invention to create a heat-transferconcentrate for heat-transfer media for storage or for transport of heatthat allows inexpensive storage of heat, is stable, nontoxic, and notexplosive, as well as indicating a process for its preparation and itsuse, and a high-capacity latent heat-storage device.

The object of the invention is therefore a heat-storage concentratecharacterized by a storage-stable dispersion of a heat-transfer mediumand at least one fine-particle and/or high-porosity solid to whichgallium has been adsorbed.

An additional object of the invention is a process for preparation ofthis heat-transfer concentrate which is characterized by the fact that aheat-transfer medium with at least one fine-particle and/orhigh-porosity solid and gallium, preferably in liquid form, are mixed,and the gallium is caused to homogeneously adsorb to the fine-particleand/or high-porosity solid as a result of mixing and the effects of thehigh mixing energy, e.g., using a high-speed homogenizer, and the solidparticles laden with gallium are homogeneously dispersed.

An additional object of the invention is a heat-transfer mixtureprepared from the heat-transfer concentrate prepared as per theinvention, as well as a heat-transfer medium.

An additional object of the invention is the use of the heat-transferconcentrate of the invention in heat-transfer mixtures for storage andtransfer of heat in reactors with heat exchangers, for use in heatpumps, and as a medium for thermochemical energy storage.

An additional object of the invention is a latent heat-storage devicecomprising a storage vessel 1, a primary heating circuit 2, a secondaryheating circuit 3 for removal of the heat latently stored in aheat-storage medium 4, characterized by the fact that the heat-storagemedium 4 consists of a heat-transfer mixture of the invention consistingof the heat-transfer concentrate of the invention and a heat-transfermedium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a latent heat-storage device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In principle, all heat-transfer media known to those skilled in the artcan be used as long as the gallium can be dispersed into it in thepresence of fine-particle and/or high-porosity solids to an adequatelyhigh extent. In particular, known liquid, crystalline, or pasty glycols,low-viscosity silicone oils, and synthetic oils can be used asheat-transfer media.

It was recognized in the invention that gallium can be dispersed intoheat [transfer] media in the presence of fine-particle and/orhigh-porosity solids to form stable dispersions.

Zeolites are preferably used as solids, especially those with a particlediameter in the range of 1-3 μm, especially from 1.5-2.1 μm, and whosepore diameters are in the range of 0.2-0.6 nm, especially from 0.3-0.5nm. Hydrophilic or hydrophobic silicon dioxide or a mixture thereof canpreferably also be used. As extremely fine particulate hydrophilic orhydrophobic silicon dioxide, commercially available AEROSIL consistingof spherical particles is used. This AEROSIL can be used in the form ofan aqueous dispersion or as a dry powder.

As fine-particle and/or high-porosity solids, preferably finely groundsilicates, aluminates, and ground plastics can also be used.

In using, for example, crystalline polyethylene glycols as heat-transfermedium for a latent heat-storage device, the heat-transfer concentrateis prepared in that crystalline polyethylene glycol is initially heatedto above its melting point and gallium is subsequently dispersed intothe liquid glycol phase as per the process of the invention using ahigh-speed homogenizer at 18,000 rpm. For example, for use in a latentheat-storage device, this heat-storage concentrate can also be mixedwith other crystalline glycols that can have a higher meltingtemperature than the crystalline glycol use for preparation of theheat-transfer concentrate. If a soft or pasty heat-transfer concentrateis desired, one can use only one low-viscosity glycol, i.e., a liquid,and subsequently mix this with crystalline glycol. Depending on themolecular weight of the glycol, one can differentiate between liquid,soft, pasty, or hard-waxy products. Liquid glycols have a molecularweight of 190-630 g/mol. Soft to hard-waxy glycols have a molecularweight of 950-35,000 g/mol. A mixture of glycols of various molecularweights can be used and can be calculated by the formula:

Molecular weight=(56,110×2)/HN

in which HN is the hydroxy number.

The use of glycols as the heat-transfer medium in latent heat-storagedevices leads to a substantially higher total stored heat compared towater, as a comparison of crystalline polyethylene glycols with watershows, for example.

Crystalline polyethylene glycols (PEG), which are neither toxic norvolatile, have a specific heat capacity in the range of 2.1-2.5 kJ/kg·K.An amount of 1,000 kg PEG can be heated to 180° C. and cooled again asoften as desired without the occurrence of technical problems [and]without losing the capacity of the aggregate to change its state. Inthis manner, an amount of heat of maximally 400 MJ (at 20° C. startingtemperature) can be stored. If one considers that upon removal of thestored heat, the heat of melting or solidification of 167-212 kJ/kgliberated during the liquid-to-solid phase transition with 1000 kg ofheat-storage medium consisting of PEG, a total stored heat of 612 MJ=170kWh can be recovered. By contrast, with the same 1000 kg amount ofwater, a filling temperature of 12° C., and a final temperature of 82°C., only 293 MJ=81.454 kWh can be stored.

The disadvantage of the lesser thermal conductivity of the glycols (0.22W/mK) compared to water (0.57 W/mK) is not only eliminated by thepresence of the dispersed gallium in the heat-transfer concentrate ofthe invention which is later to be mixed with the heat transport mediumof the same kind, but the thermal conductivity of the heat-transfermedium can be adjusted to a higher level (>1 W/mK) than water dependingon the degree of enrichment with gallium. In preparation of theheat-transfer mixtures of the invention, in order to keep the amounts ofheat-transfer concentrate of the invention to be added to theheat-transfer medium as low as possible, the heat-transfer concentrateof the invention should have as high a proportion of gallium aspossible. This means that in the process of the invention forpreparation of the heat-transfer concentrate, gallium can be dispersedinto the heat-transfer medium in the presence of fine-particle and/orhigh-porosity solids to the point of saturation.

In preparation of heat-transfer concentrates using, for example, liquidglycols, dispersing can be done in the presence of dispersing aids. Thechoice of dispersing aid is a function of the heat-transfer medium withwhich the heat-transfer concentrate of the invention will later bemixed. If, for example, the latent heat-storage device is to be operatedwith liquid glycol, for example, low-viscosity glycols such asdiethylene glycol or triethylene glycol or glycol ethers, for example,ethylene glycol monobutyl ether, are suitable as dispersing aids. Ifsilicone oils or synthetic oils are chosen as heat-transfer medium foruse in the latent heat-storage device, then low-viscosity silicone oils,for example, Baysilon M5 or M50 from Bayer AG are suitable as dispersingaids, or in using synthetic oils, heat-transfer oils such as Transal 593from BP, Marlotherm from Huls AG, or Santotherm from Monsanto [aresuitable] which can then be appropriately mixed with higher viscositysilicone oils or synthetic oils [respectively].

In the preparation of a heat-transfer mixture from the heat-transferconcentrate of the invention and a heat-transfer medium, the totalamount of gallium in the heat-transfer mixture is not critical and inprinciple, any desired mixture of the heat-transfer concentrate of theinvention and the heat-transfer medium could be adjusted, however,advantageous results are obtained if the heat-transfer mixture isadjusted in such a manner that one liter of heat-transfer mediumcontains 2-8 g of the heat-transfer concentrate of the invention which[in turn] contains approximately 50 wt % or more gallium.

It was found, surprisingly, that gallium metal, with a low melting pointof 29.6° C., can be processed into storage-stable dispersions in theheat-transfer medium, preferably glycols, low-visosity silicone oils,and synthetic oils, in the presence of fine-particle and/orhigh-porosity solids with a high-speed homogenizer.

In order to obtain a homogeneous dispersion, the speed of the mixingblade of the high-speed homogenizer is approx. 18,000 rpm.

The dispersing time in the homogenizer is preferably 5 min.

The heat-transfer concentrate of the invention can be further stabilizedby addition of anionic and/or cationic surfactants, polyacrylic acids,and gels, which in the crude state, e.g., of a heat-transfer fluid, forma lattice structure which breaks down in the agitated state, but theviscosity of the heat-transfer fluid is not affected.

Although in using zeolites for additional stabilization of thedispersion of the heat-transfer concentrate of the invention, it isadvantageous to use Rhodopol (an anionic polymer that is soluble inethylene glycol at 65° C., guar meal, and/or carob meal, especially in aweight ratio of Rhodopol to carob meal of 60:40; in using extremely fineparticulate hydrophilic and/or hydrophobic silicon dioxide, the additionof further stabilizing agents is not needed since a very good storagestability of the gallium dispersion is obtained even without additionalstabilizing agents.

As microscopic studies have shown, in dispersing of gallium in thepresence of zeolites in the heat-transfer fluid, the gallium is pressedthrough the pores of the zeolite and the zeolite particles aresurrounded by the gallium particles at an extremely thin wall thicknessso that there is a barely measurable increase in the size of the zeoliteparticles.

In a further embodiment of the invention, graphite powder of particlesize ≦5 μm can also be dispersed into heat-transfer concentrate duringits preparation to improve the thermal conductivity. The graphite powdercan be added to the homogenizer and dispersed at approximately 18,000rpm in preparing the heat-transfer concentrate of the invention. Inusing crystalline glycols, these are melted prior to dispersing [of thegraphite].

Since especially the use of crystalline glycols (PEG) permitstemperatures greater than 100° C., oxidation stabilizers can be added toprevent oxidation of the glycols. These can be chosen from amongtrimethyldihydroquinoline, diphenylamine derivatives, phenothiazine, andphenyl-α-naphthylamine.

In a further advantageous embodiment of the invention, the heat-transferconcentrate can also contain a gallium alloy; in particular, by choiceof a suitable gallium alloy, the melting point can be adjusted in such amanner that it agrees with the melting point, for example, of thecrystalline glycol used as the heat-transfer medium, or that it lies inthe average working temperature range or higher of the heat-transfermedium of a collector so that upon removal of energy from the latentheat-storage device, the heat of solidification of the gallium alloy isrecovered in addition to the heat of solidification of the crystallineglycol.

In preparation of the heat-transfer concentrate of the invention, it isobserved that during the first 5 min of homogenization of the gallium inthe presence of zeolites in the heat-transfer fluid, there is a linearincrease in the temperature, whereas after approximately 5.5 min, onecan detect a temperature increase that proceeds nearly exponentially.This phenomenon can be traced to the occurrence of heat of adsorptionduring the adsorbing of the gallium onto the zeolite and can also beexpected for extremely fine-particle hydrophilic and/or hydrophobicsilicon dioxide or other fine-particle solids. In this, the point intime of the appearance of the heat of adsorption is determined by thestirring energy (revolutions/minute), the mass of zeolite, the mass ofgallium, and the viscosity of the heat-transfer fluid.

Since gallium is desorbed from the zeolites during heat addition to aheat exchanger (this can also be expected for other fine-particle and/orhigh-porosity solids), the heat-storage medium of the invention can alsobe advantageously used for thermochemical energy storage.

The use of the heat-storage medium of the invention in heat pumps ispromising since an additional energy gain can be obtained from the heatof melting (heat of solidification) due to the low melting temperatureof 29.6° C.

The heat-storage medium of the invention can be used for storage andtransport of heat in reactors with heat exchangers and for use in heatpumps.

A latent heat-storage device as per the invention is shown in FIG. 1. Itconsists of a storage vessel 1, a primary heating circuit 2, a secondaryheating circuit 3 for removal of the heat latently stored in aheat-storage medium 4, wherein the heat-storage medium 4 consists of aheat-transfer mixture of the invention which consists of theheat-transfer concentrate of the invention in admixture with aheat-transfer medium which can advantageously be chosen from liquid,crystalline, or pasty glycols, low-viscosity silicone oils, or syntheticoils.

The invention is described in more detail below on the basis ofexamples.

EXAMPLE 1

Preparation of a heat-transfer concentrate for use in a heat-storagemedium based on glycol

If the heat-storage medium is based on glycol, ethylene glycol monobutylether is filled into a homogenizer with a capacity of 1 L in combinationwith diethylene glycol and/or triethylene glycol as dispersing liquid(heat-transfer fluid), for example, in the following amounts:

    ______________________________________                                        Triethylene glycol   200        mL                                            Ethylene glycol monobutyl ether                                                                               mL 50                                         Zeolite with a particle size of                                                                               <4                                                                            μm                                         and a pore size of approximately                                                                              nm.4                                          (Wessalith NP from Degussa)                                                                                   g      20                                     Silica (e.g., AEROSIL from Degussa)                                                                           2                                                                             g                                             Gallium                         g                                             ______________________________________                                                                        200                                       

In order to obtain a homogeneous dispersion, the speed of the grindingbade of the high-speed homogenizer is set to approximately 18,000 rpm.The dispersing time in the homogenizer is preferably 5 min.

This heat-transfer concentrate is then added, depending on the desireddegree of enrichment, in amounts of 2, 4, or 8 g or more per liter to achosen heat-storage medium based on glycol. Such a heat-storage mediumcan be, for example, Glythermin P44, Glythermin NF, or Glythermin 200from BASF. By mixing of the heat-transfer concentrate of the inventioninto a heat-storage medium, a heat-transfer mixture of the invention isobtained that can be used, for example, in a latent heat-storage device.

For further storage stabilization of the gallium particles in theready-to-use, low-viscosity heat-storage medium, an anionic polymer, forexample Rhodopol xanthan, can be added in an amount of 0.5 g per literof heat-storage medium. Mixing of the heat-transfer concentrate of theinvention with a heat-storage medium can be done with conventionalstirring equipment, that is, homogenization of the concentrate in theheat-transfer mixture in a high-speed homogenizer is no longer needed.

If pasty or crystalline glycols, for example polyethylene glycol (PEG),are used as heat-storage medium in a latent heat-storage device forstorage of heat energy, dispersing of the gallium is done as describedabove. The low-viscosity glycol such as diethylene glycol or triethyleneglycol only alters the molecular weight of the PEG to a slight extent sothat the advantage of higher heat-storage from PEG as a result of theheat of melting or solidification of 167-207 kJ/kg glycol during thephase transition can be extensively retained and exploited. Although ithas been shown that 2-8 g of the heat-transfer concentrate of theinvention (with a weight proportion of approximately 50% or more ofgallium) per liter heat-storage medium leads to an adequate increase ofthe thermal conductivity of, for example, crystalline glycols, thoseskilled in the art can also choose other ranges here as desired. Inaddition, graphite with a particle size of <5 μm can also beincorporated into the heat-transfer concentrate of the invention or theheat-transfer mixture of the invention.

EXAMPLE 2

Heat-transfer concentrate based on silicone oil

    ______________________________________                                        Silicone oil (Baysilon M5)                                                                         200        mL                                            Zeolite with a particle size of                                                                               μm                                         and a pore size of approximately                                                                              nm0.4                                         (Wessalith NP from Degussa)                                                                                   g       20                                    Silica (e.g., AEROSIL from Degussa)                                                                           g2                                            Gailium                         g                                             ______________________________________                                                                        200                                       

This concentrate obtained after treatment in a high-speed homogenizer asin Example 1 can then be further processed to produce a heat-storagemedium of the invention with other commercially available conventionalsilicone oils.

EXAMPLE 3

Concentrate based on heat-transfer oils (synthetic oils)

One proceeds in the same manner as in Example 1, however a heat-transferoil is used as the dispersing liquid into which the gallium is dispersedto prepare the heat-transfer concentrate of the invention. As dispersingliquids, heat-transfer oils such as Transal 593 from BP, Marlotherm fromHuls AG, or Santotherm from Monsanto are suitable.

EXAMPLE 4

Preparation of a heat-transfer fluid containing stable dispersed gallium

Although is it simpler to prepare a heat-storage mixture of theinvention by mixing a heat-transfer concentrate of the invention with aheat-storage medium, a stable dispersion of a heat-storage medium andgallium can also be prepared directly (suitable when small amounts aredesired) without previously preparing the heat-transfer concentrate ofthe invention.

For this purpose, 4 g zeolite and 5 drops gallium are added to 200 mLheat-transfer fluid (glycol) with the aid of a pipette in a laboratoryexperiment. The weight of gallium is approximately 1 g. Subsequently[the mixture] is dispersed in a high-speed homogenizer at 18,000 rpmuntil the heat-transfer fluid has a uniform anthracite-black color aftera dispersing time of 5 min. A surface distribution of gallium particlesof approximately 2000 m² is obtained.

In another laboratory experiment, 0.8 g extremely finely dividedhydrophobic silicon dioxide (AEROSOL [sic; AEROSIL]) and 5 drops ofgallium are added to 200 mL heat-transfer fluid (low-viscosity siliconeoil) with the aid of a pipette. The weight of the gallium isapproximately 1 g. Subsequently [the mixture] is dispersed with ahigh-speed homogenizer at 18,000 rpm until the heat-transfer fluid has auniform anthracite-black color after a dispersing time of 5 min. Astable gallium dispersion is obtained.

We claim:
 1. A heat-transfer concentrate comprising a storage-stabledispersion of a heat-transfer effective amount of a heat-storage mediumand a heat-transfer effective amount of gallium wherein the gallium isadsorbed onto a solid having either a particle diameter of 1 to 3 μm ora pore diameter of 0.2 to 0.6 nm, or both.
 2. The heat-transferconcentrate of claim 1, wherein the heat-storage medium is selected fromthe group consisting of glycol, silicone oil, synthetic oil, and amixture thereof.
 3. The heat-transfer concentrate of claim 1, whereinthe solid comprises a zeolite.
 4. The heat-transfer concentrate of claim3, wherein the zeolite has a particulate diameter of 1.5 to 2.1 μm. 5.The heat-transfer concentrate of claim 3, wherein the zeolite has a porediameter of 0.3 to 0.5 nm.
 6. The heat-transfer concentrate of claim 1,wherein the solid comprises a hydrophilic or hydrophobic silicondioxide, or a mixture thereof.
 7. The heat-transfer concentrate of claim1, wherein the solid comprises silicate.
 8. The heat-transferconcentrate of claim 1, wherein the solid comprises aluminate.
 9. Theheat-transfer concentrate of claim 1, wherein the solid comprises groundplastic.
 10. The heat-transfer concentrate of claim 1, furthercomprising a stabilizing agent or a dispersing aid.
 11. Theheat-transfer concentrate of claim 10, wherein the stabilizing agent isselected from the group consisting of anionic or cationic surfactants,polyacrylic acids, gels, and a mixture thereof, and wherein thedispersing aid is selected from the group consisting of glycol,glycol-ether, silicone oil and a mixture thereof.
 12. The heat-transferconcentrate of claim 10, wherein the stabilizing agent is selected fromthe group consisting of an anionic polymer, guar meal, carob meal, and amixture thereof, and wherein the dispersing aid is selected from thegroup consisting of triethylene glycol, ethylene glycol monobutyl ether,polydimethylsiloxanes and a mixture thereof.
 13. The heat-transferconcentrate of claim 12, wherein anionic polymer and carob meal arepresent in a weight ratio of 60:40.
 14. The heat-transfer concentrate ofclaim 1, further comprising a heat-transfer effective amount ofgraphite.
 15. The heat-transfer concentrate of claim 14, wherein thegraphite has a particle size of less than 5 μm.
 16. The heat-transferconcentrate of claim 1, further comprising an oxidation stabilizer. 17.The heat-transfer concentrate of claim 16, wherein the oxidationstabilizer is selected from the group consisting oftrimethyldihydroquinolone, diphenylamine derivatives, phenothiazine,penyl-a-naphthylamine, and a mixture thereof.
 18. The heat-transferconcentrate of claim 1, wherein the gallium is a gallium alloy.
 19. Theheat-transfer concentrate of claim 18, wherein the gallium alloy has amelting point of at least as high as the temperature of a heat-transfereffective amount of heat-storage medium.
 20. The heat-transferconcentrate of claim 2, wherein the glycol is crystalline polyethyleneglycol.
 21. A process for preparing a heat-transfer concentrate,comprising:a. melt mixing a heat-transfer effective amount of aheat-storage medium, a heat-transfer effective amount of a solid havingeither a particle diameter of 1 to 3 μm or a pore diameter of 0.2 to 0.6nm, or both, and a heat-transfer effective amount of gallium in liquidform; b. uniformly adsorbing the gallium onto the solid; and c.homogeneously dispersing the solid laden with gallium and the heatstorage medium.
 22. The process of claim 21, wherein the heat-storagemedium is selected from the group consisting of glycol, silicone oil,synthetic oil and a mixture thereof.
 23. The process of claim 21,wherein the solid comprises a zeolite.
 24. The process of claim 23,wherein the zeolite has a particulate diameter of 1.5 to 2.1 μm.
 25. Theprocess of claim 23, wherein the zeolite has a pore diameter of 0.3 to0.5 nm.
 26. The process of claim 21, wherein the solid comprises ahydrophilic or hydrophobic silicon dioxide, or a mixture thereof. 27.The process of claim 21, wherein the solid comprises silicate.
 28. Theprocess of claim 21, wherein the solid comprises aluminate.
 29. Theprocess of claim 21, wherein the solid comprises ground plastic.
 30. Theprocess of claim 21, wherein the solid laden with gallium is dispersedin the heat-storage medium to the point of saturation.
 31. The processof claim 22, wherein the glycol is a crystal glycol and the melt mixingstep occurs at a temperature above the melting point of the crystalglycol to form a liquid glycol phase prior to the dispersing step. 32.The process of claim 31, wherein silicon dioxide is mixed into theliquid glycol phase.
 33. The process of claim 21, wherein the gallium isa gallium alloy.
 34. The process of claim 33, wherein the gallium alloyhas a melting point of at least as high as the temperature of theheat-storage medium.
 35. The process of claim 22, wherein the glycol iscrystalline polyethylene glycol.
 36. The process of claim 21, wherein aheat transfer effective amount of graphite is further dispersed with theheat-storage medium, the solid and the gallium in the dispersing step.37. The process of claim 36, wherein graphite has a particle size ofless than 5 μm.
 38. The process of claim 23, wherein the zeolite has aparticle diameter of 1.9 μm and a pore size of 0.4 nm.
 39. The processof claim 21, wherein the dispersing step is performed with a grindingblade rotating at approximately 18,000 rpm.
 40. The process of claim 21,wherein a stabilizing agent or a dispersing aid, or a mixture thereofare further dispersed with the heat-storage medium, the solid and thegallium in the dispersing step.
 41. The process of claim 40, wherein thestabilizing agent is selected from the group consisting of anionic orcationic surfactants, polyacrylic acids, gels, and a mixture thereof,and wherein the dispersing aid is selected from the group consisting ofglycol, glycol-ether, silicone oil and a mixture thereof.
 42. Theprocess of claim 40, wherein the stabilizing agent is selected from thegroup consisting of an anionic polymer, guar meal, carob meal, and amixture thereof, and wherein the dispersing aid is selected from thegroup consisting of triethylene glycol, ethylene glycol monobutyl ether,polydimethylsiloxanes and a mixture thereof.
 43. The process of claim42, wherein anionic polymer and carob meal are present in a weight ratioof 60:40.
 44. The process of claim 40, wherein the dispersing stepoccurs for approximately 5 minutes.
 45. A heat-transfer mixture that canstore heat comprising a heat-transfer effective amount of theheat-transfer concentrate of claim
 1. 46. A heat-transfer mixture ofclaim 45, wherein the heat-storage medium is selected from the groupconsisting of glycol, silicone oil, synthetic oil, and mixtures thereof.47. A heat-transfer mixture of claim 45, wherein 2 to 8 gramsheat-transfer concentrate are contained in 1 liter of heat-storagemedium.
 48. A method of using a heat-transfer mixture, comprisingstoring and transporting heat in the heat-transfer mixture of claim 45in reactors with heat exchangers.
 49. A method of using a heat-transfermixture, comprising utilizing the heat-transfer mixture of claim 45 in aheat pump.
 50. A method of using a heat-transfer mixture, comprisingutilizing the heat-transfer mixture of claim 45 as a medium forthermochemical energy storage.
 51. A latent heat-storage devicecomprising a storage vessel, a primary heating circuit, and a secondaryheating circuit for removal of heat latently stored in the heat-transfermixture of claim 45.